Carbon Dioxide and Oxygen Partial Pressure in Expiratory Water Condensate Are Equivalent to Mixed Expired Carbon Dioxide and Oxygen

This study was to determine whether the PconCO2 and PconO, which collect in the expiratory trap of a ventilator circuit are equivalent to PĒCO2 and PĒO2. Fifty studies were performed in 34 mechanically ventilated male patients. Five milliliters of condensate fluid were collected and PĒCO2 and PĒO2 were measured. Exhaled gases were collected simultaneously with condensate fluid for 5 min in a meteorologic balloon and FĒCO2 and FĒO2 were measured; PĒCO2 and PĒO2 were then calculated. The mean PĒCO2 was not significantly different from PconCO2 nor was the PconO2 significantly different from the condensate PconO2. There was á high correlation between mixed expired PĒCO2 and PconCO2 as well as PĒO2 and PconO2. These data indicate expiratory PconCO2 and PconO2 provide a valid reflection of PĒCO2 and PEO2. The PconCO2 and PconO, measured in a clinical blood gas analyzer are accurate and may be used in calculation of Vd/Vt and in metabolic assessments.